A PMR write head typically has a main pole with a small surface area at an air bearing surface (ABS), and coils that conduct a write current and generate a magnetic flux in the main pole such that the magnetic flux exits through a main pole tip and enters a magnetic medium (disk) adjacent to the ABS. Magnetic flux is used to write a plurality of bits in the magnetic medium where the bits have various lengths that are in integer multiples of a minimum bit length T such as 1 T, 2 T, 3 T, etc. Bits are arranged in concentric tracks found in multiple radial regions that are classified as an inner diameter (ID), middle diameter (MD), and outer diameter (OD). In some schemes such as shingled magnetic recording, tracks are written in a sequential manner from ID to OD, from OD to ID, or from OD and ID towards MD.
The hard disk drive (HDD) also known as a magnetic recording apparatus has a central processor unit (CPU) and a read/write channel that encodes digital information into analog signals during a write process. There is also a preamplifier or preamp, which is a chip in the HDD that controls the read/write heads and amplifies signals to and from the heads. The main pole in the PMR write head is driven by a current waveform that generates the magnetic fields needed to write the bipolar bits in the magnetic medium. Write current waveforms are generated by the preamp and have a large impact on the dynamic magnetic field profiles during the write (recording) process. Typical waveform settings include the write current amplitude (lw), overshoot amplitude (OSA), overshoot duration (OSD), current rise time (Tr), current fall time (Tf), and write data frequency (Fw). These parameters may be tuned to adjust one or more of BPI, TPI capability, and area density capability (ADC) in the HDD. A write head that can deliver higher BPI and higher TPI is essential to ADC improvement.
As HDD technology advances, there is a need to continually shrink the main pole (MP) dimensions at the ABS in order to satisfy requirements for ADC growth. However, a certain MP tip volume is required in order to sustain sufficient writability on the media plane. Therefore, an alternative means of improving ADC through larger TPI is desirable that complements improvements achieved through new MP and surrounding shield designs. In particular, a new write scheme is needed that is compatible with MP down-track tip lengths of 50-150 nm, and with minimum bit lengths of around 10 nm.